This intensive study of the second year of life investigates the processes which shape the development of a child's internal representations of the world and of his position in it. A major objective is to trace the relationship between characteristics of behavior observed in a wide variety of representative situations during the second year and subsequent patterns of coping with the physical and social environment. Forty predominantly middle class Caucasian babies are regularly and repeatedly observed between the ages of 12 and 24 months in the course of (a) visits to the home, (b) successive hour-long playgroups, (c) developmental tests and (d) specially designed situations structured to activate attachment, curiosity, fear and effectance behavior. All but the home observations have been stored in videotape. A follow-up assessment of the children's competences at age 3 1/2 was based on observations of their behavior in a special 5-week nursery school program, during a home visit, and in a standard intelligence test situation. Analyses follow an ethological model with increasingly molar constructs being derived from profiles of special action-reaction patterns observed to be elicited in a variety of contexts by different types of social and non-social stimuli.